This invention relates to screw fasteners and prevents accidental unscrewing thereof, it being an object of this invention to safety lock the lug-nuts of vehicle wheels. While it may not happen often, loose lug-nuts are a definite safety hazard when coming loose during vehicle travel. Accordingly, most Recreational Vehicle (RV) and travel trailer owner's manuals recommend retightening lug-nuts every two hundred miles or at regular intervals, so as to prevent the hazard of losing a wheel. However, it cannot be presumed that all owners adhere to said recommendation. Therefore, it is an object of this invention to provide a Safety Lock System that reveals loose lug-nuts by simple observations of the safety lock device.
It is to be understood that there is a wide variety of screw fasteners used for a wide variety of purposes, whether they are bolts or nuts, external or internal wrenching, or with slotted or socketed drive features. The characteristic features of a male screw fastener is that the shank or body is threaded to either enter a threaded hole or to receive a nut, and is provided with a head with means to be rotated and torqued. Likewise, the characteristic feature of a female screw fastener is that the body has a threaded bore and is provided with means to be torqued. The usual bolt or nut is threaded right handedly, with various types and quality of threads. A feature of lug-nuts is that they are self locking when properly torqued, but thay do have a propensity to loosen in counter-rotation to their tightening. This loosening factor is counteracted to a great extent in vehicle wheels by employing so-called self locking lug-nuts wherein the interface of the nut and stud opening in the wheel is conical, at approximately 60.degree. (inclusive) which is a locking angle. Nevertheless, vehicle wheels are lost from time to time as a result of loosening lug-nuts.
It is a general object of this invention to prevent one or more nuts or bolts from loosening from their torqued condition, particularly lug-nuts as they are applied to the wheel mounting studs of vehicles. In practice, vehicle wheels are mounted by means of at last four or more studs and lug-nuts applied thereto, it being common practice to employ five such screw fasteners on full sized passenger cars, and for example eight on light trucks, and many more on heavy commercial equipment. In any case, these studs and lug-nuts are cooperatively secured in pairs by the present invention, each lug-nut or bolt being safety locked to prevent counter-rotation more than a very restricted part of a turn. To this end a cap is applied to each fastener or lug-nut with a tie or lanyard there-between, it being an object to prevent counter-rotation of either fastener or lug-nut thereby. A feature of this invention is the tie or lanyard and the manner of securement to each cap, being secured so that each cap is an anchor that prevents counter-rotation of the other, as later described. It is to be understood that either fastener can loosen but a part turn, at which point or position its counter-rotation is stopped. These,fasteners are threaded right or left handed.
It is an object of this invention to provide a safety lock device for screw fasteners of the type hereinabove referred to that is reusable. Decorative caps and the like have been applied by means of press fits and various forms of clips and the like, a positive form of such fastener being an object of this invention. Accordingly, resilience of the cap is employed to snap a detent member into a notch provided on the lug-nut per se. In practice, a conventional hexagonal, six faced, external wrenching lug-nut is employed, with a detent notch in each face.
It is also an object of this invention to control and/or stop counter-rotation of either of a pair of multi-faced and preferably hexagonal fastener heads such as lug-nuts. A preferred permissible part turn of loosening is 20.degree. as determined by the lanyard length that limits said rotation while permitting installation of a pair of connected caps to next adjacent fasteners or lug-nuts, regardless of their rotational positions when properly torqued, all of which is described.
It is still another object of this invention to guide a safety lock device in the form of a cap of the type hereinabove referred to, so that it axially aligns with a projecting stud. Commercial and heavy duty wheel constructions involve replaceable stud units characterized by threaded studs that project through and extend beyond the installed position of the lug nuts (see FIG. 14). Thus, the cap of the present invention is elongated to accomodate said stud extension and is subject to misalignment. Accordingly, the cap is provided with guide ribs, and also with thread engageable retainer means.